The first-round turnout of 78.92% on October 4 sets the baseline for the October 25 runoff, with abstention at 21.08%—the highest first-round rate since 1998—driven by voter disillusionment, polarization between the PT and PL camps, demographic shifts toward older voters, and the ease of justifying absence under Brazil’s rules. Traders price the 78-80% band highest because runoff mobilization by Flávio Bolsonaro and Lula has historically produced only modest gains in participation amid persistent apathy, especially among lower-income and less-educated groups. Recent polls showing a tightening race have not yet triggered widespread expectations of a sharp turnout spike, while blank and null ballots from the first round further signal structural disengagement that campaigns must overcome in the narrow window before the vote.